1. Field of the Invention
The present invention relates to a method for manufacturing a camshaft and a mandrel for use in the method.
2. Related Art
A method for manufacturing a camshaft by expanding and jointing a cam lobe (or cam piece) and a hollow shaft (e.g., a tubular member, a shaft tube or a pipe) is known to provide excellent results in lightening the camshaft structure for high-speed rotation and low fuel consumption and in reduction of exhaust emissions for protecting the environment. Publications relating to the invention will be enumerated in the following.
Publication (1); Examined Published Japanese Patent Application No. 46-21299 relating to a method for shaping a camshaft. There is disclosed a structure in which a shaft tube and a cam, a journal or the like are jointed by setting the cam, the journal or a shaft head in a split mold, by inserting the shaft tube into the axial hole of the journal and by radially enlarging (or expanding) the shaft tube through a die (or mandrel). This structure is intended to manufacture the camshaft easily through the split mold and the die and to lower the manufacture cost.
Publication (2): Unexamined Published Japanese Patent Application No. 5-288014 relating to a camshaft. There is disclosed a structure in which the camshaft is assembled from a camshaft made of a sintered alloy and a camshaft made of a steel pipe by constructing an inner piece and a hollow shaft of an easily expandable steel and by expanding and jointing them with a high-pressure fluid and a mandrel. This structure is intended to lower the assembly cost and to prevent the cam piece from being broken during assembly and in use.
Publication (3): Unexamined Published Japanese Patent Application No. 53-102861 relating to a method for jointing a ring to a hollow shaft. There is disclosed a structure in which the ring (or cam) on the hollow shaft is fixed in the tuning direction and in the axial direction by forming paddings on the two sides of the ring of the hollow shaft.
Publication (4): Unexamined Published Japanese Patent Application No. 8-158817 relating to a method for manufacturing an assembly-type camshaft. There is disclosed a structure in which a projection of a shaft is registered with a groove of a cam (or cam lobe) and is bulged and press-fitted in the groove by expanding the shaft. This structure is intended to fix the cam firmly.
Publication (5): Unexamined Published Japanese Patent Application No. 9-100703 relating to an expansion assembly type of hollow camshaft. There is disclosed a structure in which a hollow shaft and a cam lobe are integrally jointed and assembled by knurling the hollow shaft and by expanding the hollow shaft through a mandrel having a worked head of a splined sectional shape to join and integrate the knurled portion and the cam lobe during the expansion. This structure is intended to work the inner circumference inexpensively with high accuracy and to lower the cost while preventing the cam lobe from being broken.
In Publication (1), no special means is provided in the shape and operation off the die. As a result, the expanded shaft tube may often be temporarily constricted to loosen the joint between the shaft tube and the cam, the journal or the like, once jointed. Since the inclination angle of the die is arbitrary, on the other hand, there may be drawing residuals at the time of expansion, and the shaft tube may be elongated. This leaves an unsolved problem, that a camshaft of high accuracy cannot be manufactured.
In Publication (2), the cam piece is provided with the inner piece, and the inner piece and the shaft are provided with radially larger and smaller portions. As a result, the structure is complicated and leaves unsolved the problem that the camshaft cannot be provided at a low cost. Here, this structure is not devised on the inclination angle of the mandrel so that it seems to have a problem similar to that of Publication (1).
Publication (3) provides the relation between the paddings of the hollow shaft and the ring (or cam). However, there are no means for preventing the expanded pipe from returning or for the inclination angle of the mandrel. Here, this structure seems to have a problem similar to that of Publication (1).
Publication (4) provides a structure for bulging and press fitting the projection into the groove of the cam (or cam lobe) by expanding the shaft. However, there are no means for preventing the expanded pipe from returning or for the inclination angle of the mandrel. Here, this structure seems to have a problem similar to that of Publication (1).
Publication (5) provides a structure for joining and integrating the knurled portion and the cam lobe during the expansion. There is no device for preventing the expanded pipe from returning. As a result, this structure seems to have a problem similar to that of Publication (1). On the other hand, the mandrel of the structure has the worked head of the splined sectional shape. However, there is no device for the inclination angle. Here, this structure seems to have a problem similar to that of Publication (1).
It is, therefore, an object of the invention to solve the problems of the prior art, as specified in connection with the publications.